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TABLE 1. Vertebrate faunal list of the Arlington Archosaur Site. Data from Noto (2015), Adams et al. (2017), Adrian et al. (2019, 2021), and Noto et al. (2019, 2022).

  Hybodontidae indet.
  Cretodus sp.
  Squalicorax sp.
  Onchopristis dunklei
  Pseudohypolophus (Hypolophus) mcnultyi
  Pseudomyledaphus sp.
  Melvius sp.
  Elopomorpha indet.
  Coelodus sp.
  Enchodus sp.
  Lepisosteidae indet.
Osteichthyes - Dipnomorpha
  Ceratodus carteri
  Caudata indet.
  Cryptobranchidae indet.
  Anura indet.
Reptilia - Dinosauria - Theropoda
  Tyrannosauroidea indet.
  Carcharodontosauria indet.
  Ornithomimosauria indet.
  Dromaeosauridae indet.
  Troodontidae indet.
  Coelurosauria indet.

Reptilia - Dinosauria - Ornithopoda

  Protohadros byrdi
Reptilia - Crocodyliformes
  Deltasuchus motherali
  Scolomastax sahlsteini
  Woodbinesuchus byersmauricei
  Terminonaris cf. robusta
  Eusuchia indet.
Reptilia - Testudinata
  Naomichelys sp.
  Gehennachelys maini, comb. nov.
  Pleurochayah appalachius
  Trionychidae indet.
  Multituberculata indet.




TABLE 2. Comparison of traits from basal baenids and basal baenodds with known skulls, carapaces, and plastra. Data obtained from: Gilmore, 1920; Brinkman, 2003; Lyson and Joyce, 2009a; Joyce and Lyson, 2015; Lively, 2015; Joyce et al., 2020; Rollot et al., 2022a, b.

Trait Lakotemys
Gehennachelys maini comb. nov. Arvinachelys
Age Berriasian-Valanginian Aptian-Albian Cenomanian Campanian
Parietal-squamosal contact Present Present Absent Absent
Nasals Slightly reduced Reduced Reduced or absent Enlarged
Squamosal processes Not elongated Elongated Elongated Not elongated
Upper temporal emargination: visibility in dorsal view of anterior portion of otic capsule Not visible Not visible Visible Visible
Crista supraoccipitalis: anterior coverage by parietals Halfway Extensive Minimal Extensive
Jugal contribution to posterior orbital margin Absent Absent Present Present
Relative size of frontals and parietals Parietals larger Parietals larger Parietals larger Frontals larger
Midline extragular contact Absent Absent Present, relatively short Gular scales absent
Larger plastral lobe Anterior Posterior Equidimensional Posterior
Plastral length (cm) ~28 ~29 36.3 29.1
Vertebral scale 1 narrowing ? Posteriorly Posteriorly Posteriorly
Vertebral scale 3 dimensions Equidimensional Wider than long Wider than long Wider than long
Femoral-anal sulcus shaped Straight ? Straight Omega-shaped
Vertebral scale contribution to posterior margin Probably absent Probably absent Absent Present





TABLE 3. Relative proportions of complete baenid taxa, plus Glyptops. * indicates estimation of nearly-complete shell. Data from: Archibald (1977, table 53); Lyson and Joyce (2009b, figure 6); Larson et al. (2013, figure 21.5); Joyce and Lyson (2015: figure 2A); Lively (2015, figures 5C, 6C); Lyson et al., (2016, figure 4); Lyson et al., (2019, figure 6).

Taxon Anterior lobe length /
Posterior lobe length
Plastron length /
Carapace length
Glyptops 1 0.92 0.88
Glyptops 2 0.77 0.88
Trinitichelys hiatti 0.66 0.87
Neurankylus eximius 0.86 0.72
Thescelus insiliens 1.06 1.00
Plesiobaena antiqua 0.79 0.91
Boremys pulchra 1.18 0.89
Scabremys ornata 0.98 0.92
Denazinemys nodosa 0.91 0.91
Eubaena cephalica 1.00 0.83
Baena arenosa 0.94 0.89
Chisternon undatum 1.02 0.89
Gehennachelys maini comb. nov. 0.98 1.00
Saxochelys gilberti 1.04 1.07
Arvinachelys goldeni 0.85 0.97
Palatobaena cohen 0.60 0.94
Neurankylus lithographicus 0.84 0.81
Cedrobaena brinkman* 0.60 0.89
Neurankylus baeuri 0.84 0.80

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